Introduction
A number of testing procedures have been devised to determine how much a person can remember. Much information about short-term memory
has been obtained through a set of recall tasks in which the subject is presented with items to be recalled. Basically, the short-term memory system is of limited capacity; information is maintained by continued attention and rehearsal (the repetition of memory items). The information in short-term memory may be lost through displacement by incoming information or lost through decay with time; information in short-term memory can also be transferred to long-term memory. The experimental design can be modified to examine different aspects of short-term memory.
Recall and Recognition Tests
In the free recall technique, subjects are presented with items at a fixed rate of presentation; several trials take place, in which the order of presentation is randomized. Recall refers to the retrieval of information from memory, with or without clues.
The important feature of free recall is that subjects are allowed to remember the items in whatever order they wish. In ordered recall tasks, the subjects can report the items in any order, but they must also identify the position of their presentation. The oldest of all the techniques that involve learning a list of items is serial recall, or serial learning. In serial learning, the subject is shown one word from a list at a time, for a limited amount of time, such as two seconds per word. The second time that the list is presented, it is presented one word at a time, and the subject’s task is to remember the upcoming word in the series. In some experimental procedures, the list is repeated until the subject can accurately remember every item. In others, the list is presented a fixed number of times.
In probe recall tasks, by comparison, the subject is required to recall particular elements in a sequence of items. A common example of this is the paired-associate technique of list learning, in which subjects are shown pairs of items. The first item in the pair is called the stimulus, and the second is called the response. Recall is tested by showing the stimulus item only, requiring the subject to remember the response. The paired-associate and serial learning techniques both allow the experimenter to have considerable control, in that subjects have only one possible correct response, a limited time in which to make it, and a specific cue to aid in recall.
In another variation of list learning, called distractor recall, a subject is presented with a set of stimulus items, one item at a time. Each item is presented for a fixed period of time. Once each item has been presented a single time, a short period may follow during which the subject is asked to do an irrelevant task. The purpose of the irrelevant task is to create a delay between presentation of the stimulus items and the test to minimize the subject’s mental repetition of the items. One such task would be to require the subject to count backward, such as by threes (986, 983, 980, and so on), from a predetermined starting point. Finally, the subject is given a test to determine how many of the original items are remembered.
In general, it is more difficult to test recognition than to test recall. Recall, at least when lists of words are used, is easily scored. When recognition (noticing that information is familiar) is tested, however, the old items must be mixed with new items so that the subjects can indicate which they have seen before. One method of testing recognition is to present the old item with one or more new items and require the subject to select one which he or she believes to be the old item. In such tests, the proportion of items correctly identified as having been seen before decreases as the number of alternatives increases. Accuracy also decreases if the alternatives are similar to the originally presented items. Even when recall is perfect, the time required to produce a response varies. Latency in giving a response can also provide information about the memory processes when performance is close to perfect, making the amount recalled an inappropriate measure. Even when recall is less than perfect, time latencies can reveal underlying differences in memory processes.
Testing Long-Term Memory
Experimental tests have also been designed to study long-term memory. Long-term memory refers to the storage area that holds permanent memories and is unlimited in capacity. There is overlap between short-term memory and long-term memory, so a test that requires subjects to recall a list of words will include an assessment of both short-term and long-term memory. For example, words at the end of the list will be in short-term storage, while words at the beginning of the list might have entered long-term storage. Two major forms of long-term memory are episodic memory and semantic memory. Episodic memory involves information about where and when some event occurred. In contrast, semantic memory contains stores of words and coded categorical information.
Researchers seeking to determine the characteristics of long-term memory present subjects with tasks that require decisions about the meaning of words. In a semantic decision task, the subject is asked to decide whether the word is a member of a particular category; the phrase “Tigers are felines” might be presented, and the subject would be asked for a true/false decision. In a lexical decision task, the subject decides whether a string of letters forms a word.
Memory Organization Research
A number of studies have been described that are concerned with short-term and long-term memory. Memory research has also included diverse studies of the effects of prior activities, everyday activities, sensory modalities, perfect memories, pathological memory losses (caused by surgery, amnesia, or drug usage), and old age on memory.
Memory experiments have been conducted using materials such as cards, pencils, paper, and stopwatches. More complex techniques control the speed of presentation with computers programmed to present material visually or verbally; there are appropriate response-recording keys for voice response or finger press, which analyze the recall correctness as well as the speed of response. Experiments on memory have been conducted with animals, such as pigeons, rats, and primates, as well as with humans.
Laboratory studies of long-term memory organization are of particular interest for real-world applications. Many of these studies use categorized lists of words. The lists often consist of words from the same natural category, such as dog, cat, horse, and sheep from the category “animal.” A list might contain forty words with eight words from five categories. Subjects remember categorized lists better than uncategorized ones. Categorized lists are also remembered better when they are presented in blocks rather than when presented randomly. Blocked presentation refers to the fact that all items from a particular category are presented one after another, and then items from another category are presented. In comparison, with random presentation, the items from different categories are completely mixed in the presentation order. Blocked presentation is much more organized than random presentation. The superior memory for blocked presentation suggests the important role that organization plays in memory.
A further indication of the importance of organization is the finding that people actively rearrange randomly presented lists. That is, even though items from various categories are presented in random order, subjects tend to group the items into their appropriate categories at recall. That is, the items are recalled by category in spite of having been presented randomly. Examining the order of recall led researchers to the realization that learning and memory are influenced by the active strategies of the subject and by the properties of the learning material that allow organization to take place. When the lists consist of a set of items from a limited number of semantic categories (for example, marine animals and means of transportation) scattered throughout the list, words from each category tend to be recalled together. A number of researchers in cognitive psychology have used these principles for real-world applications. For example, knowing that people tend to recall information in these ways, educators who write textbooks can organize information in ways that will enhance the human memory system. In addition, understanding human memory helps human-factors psychologists devise techniques for the display of information on computer screens (computer interfaces) that make computer presentations more compatible with the way people learn and remember. Furthermore, in this technological age, people commonly need to search through large amounts of information to find what they are seeking. Using what is known about memory, psychologists are working to devise systems for searching large databases, such as computerized card catalogs in libraries, that work in conjunction with the way people search their own memories.
The importance of the relationships among separate elements has also been illustrated with nonverbal materials. It has been shown, for example, that simple line drawings of parts of the face are difficult to recognize when presented separately. The same drawings, however, are quickly recognized when presented in the context of a face. Additional information is provided by the context—the face, in this case—which aids the recognition of each separate element. Organization in the form of relationships among elements is important to the process of storing information in memory. This research has applications in the area of artificial intelligence. It is helping scientists to program computers to recognize human handwriting, fingerprints, and other complex stimuli.
Biological Aspects of Memory
Studies on memory that are of a biological nature have also helped psychologists who are concerned with determining how specific parts of the brain are related to the processes underlying the various types of memory. For example, both external and internal stimuli are perceived by an organism as experiences. The organism converts these experiences to a form that the nervous system can understand; they must be stored in an electrical or molecular form in the brain. An understanding of the biological processes involved has helped psychologists devise tests that are used to assess memory deficits. A memory deficit might be caused by a head injury, tumor, or disease such as Alzheimer’s disease. Researchers continue to search for clues that will help people with memory deficits to overcome those deficits by means of drug therapy or surgical repair.
Evolution of Research
Plato thought of memory as something like a block of wax. Aristotle considered the heart to be of primary importance in the memory process. Other ancient Greeks argued that the brain was the seat of memory. Although thinkers have been interested in memory for thousands of years, it was not studied experimentally until fairly recently. Research on human memory was greatly influenced by the work of European psychologists more than a century ago.
The first controlled experiments on memory were conducted in Europe by Hermann Ebbinghaus
in 1885. Ebbinghaus was engrossed in finding out how much verbal material that was well learned would be saved by his own memory over a period of time. He served as his own subject. The number of trials required to relearn a list, compared to the time to learn either a new list or the list when it was first acquired, provided a measure of the saving in learning. This experimental method has rarely been used since his time.
In 1890, William James, an American, included a chapter on memory in his renowned book on psychology. Frederic C. Bartlett, in 1932, began a tradition of studying how memories change over time. After Bartlett’s time, the primary experimental strategy became to have subjects learn lists of items, such as nonsense syllables, nouns, or adjectives. The concentration on list learning comes from the early theoretical background, which assumed that memory was built from associations. Behaviorists, such as B. F. Skinner, elaborated on memory as one of many parameters involved in learning; they treated the learning process as the association of responses to stimuli. Repeated exposure to stimuli and responses could strengthen the association between them; forgetting was thought to be a weakened association.
Since the advent of the information-processing approach in psychology in the 1960s, a large number of theories and models of memory have been proposed, including the dual-process theory, the levels-of-processing theory, the neurobiological two-phase model, and the neurobiological four-phase model. The experiments that have been conducted on memory have emerged from these unique theoretical approaches. No matter what the theoretical approach, a constant problem facing the psychologist who studies memory is the need to conduct tests using situations that are similar enough to daily life so that the results can be generalized beyond the laboratory, while allowing enough control to be maintained so that scoring can accurately show the effect of the experimental variables.
Bibliography
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